Abstract:
A method for the recovery of gold from the electroplating waste water effluents has been developed based on its adsorption on orange peel. Adsorption of gold(III) from dilute solutions of hydrochloric acid on orange peel has been studied under various experimental conditions by using batch technique. Distribution coefficients, Kd and % extraction were determined for the orange peel-gold solution system as a function of contact time, pH, sorbent, sorbate concentrations and temperature. The uptake of gold by raw orange peel is time, pH, initial metal concentration, sorbate dose, and temperature dependent. Adsorption data have been interpreted in terms of Langmuir and the Freundlich equations. Thermodynamic parameters for adsorption of gold on raw orange peel have been determined at three different temperatures. The positive value of heat of adsorption; ΔH° = 61.85 kJ/mol shows that the adsorption of gold on orange peel is endothermic whereas the negative value of ΔG° = -35.85 kJ/mol at 308 K shows the spontaneity of the process. ΔG° becomes more negative with increase in temperature which shows that the adsorption is more favorable at higher temperatures. Under the optimal adsorption conditions the adsorption capacity of gold is 5.79 mg/g of the raw orange peel out of which 5.37 mg of gold gets desorbed with 0.1 % thiourea solution.
